The present invention relates generally to the field of indicating circuits for use in automotive alternator battery charging systems. More particularly, the present invention relates to indicating circuits which provide visual indications of the malfunctioning of an automotive alternator battery charging circuit whose output is controlled in response to sensed battery voltage by a voltage regulator.
Voltage regulator controlled automotive alternator battery charging systems are commonly used in automotive electrical systems to provide for keeping an automotive storage battery at a full charge level. These type of systems function by a voltage regulator controlling the field coil excitation of an alternator in response to sensed battery voltage wherein the output of the alternator is full wave rectified and utilized to maintain the charge on the storage battery. In such systems, an indicator lamp is typically used to provide an indication of 0 alternator output so as to alert the operator of the automobile to a malfunctioning of the battery charging system. In some of these systems, the DC current which is utilized to provide a low alternator output indication before rotation of the alternator rotor carrying the field coil has commenced is also utilized to supply the alternator field coil excitation. Examples of prior systems of this type are shown in U.S. Pat. No. 3,365,646 and 3,138,751, both of which are assigned to the same assignee as the present invention. In these prior systems, the use of the lamp excitation current to also supply the initial field coil excitation minimizes the number of electrical connections necessary for the battery charging system. However, typically these type of charging systems only provide a visual indication of alternator malfunction in response to a low alternator charging output signal.
Some prior art systems have recognized the need for providing a visual indication of an excessively high alternator output voltage which is therefore indicative of a malfunction of the alternator battery charging system. U.S. Pat. No. 3,673,588, assigned to the same assignee as the present invention, is an example of one of these systems in which separate sensing circuits are utilized to separately excite different lamps so as to indicate both high and low voltage conditions. In addition, some prior systems such as that shown in co-pending U.S. Patent Application Ser. No. 038,965, filed May 14, 1979, entitled "Alarm Circuit for Automobile Alternator" and assigned to the same assignee as the present invention, contemplate the use of a single lamp for providing a single visual display indicative of either low or high alternator voltage output conditions.
In the prior systems which utilize a plurality of indicating lights, this requires an additional indicator light be provided on the dashboard of the automobile and the provision of this additional lamp is generally considered to be undesirable for aesthetic reasons as well as since additional complex circuitry may have to be utilized for providing the proper excitation to the over voltage light as well as for providing a mechanism for testing the over voltage light to ensure that it is in operating order. Thus circuitry must exist to insure (test) that this light is not burned out, since typically the light would only come on during a high voltage failure mode.
The prior art systems which utilize a single light to indicate both low and high alternator outputs have the disadvantage in that the operator of the automobile has no indication if the alternator malfunction is caused by an excessive alternator output or a deficient alternator output. In the case of an excessive alternator output, prolonged operation of the charging system in this mode can readily result in damage to the battery and alternator due to over charging of the battery and the generation of extremely large alternator voltages. This is to be contrasted with prolonged operation of the alternator battery charging system when the alternator output is found to be deficient. In this latter mode, the only danger is that the battery will eventually discharge after prolonged usage. Thus, unles the operator of the automobile is aware of which type of alternator malfunction has occurred, he may unknowingly risk damage to the alternator and battery by attempting to continue to drive the automobile while the charging system has malfunctioned.
Some prior systems have illustrated separate plug in test modules in which high and low alternator output failure modes are indicated by a flashing test light, separate from the dashboard mounted lamp which supplies initial field excitation, while other failure modes are indicated by continuous illumination of the test light. These systems require disconnection of the dashboard lamp, and fail to differentiate between high and low output failures.